Reusable storage phosphor for radiation therapy dosimetry. Abstract Modern radiation therapy has advanced considerably in the last decade with the development of improved imaging and conformal dose delivery techniques. With the subsequent increased complexity of treatment planning and dose delivery, there has been growing demand for multi-dimensional quantitative dose delivery validation. Radiographic film has become the de facto standard for two-dimensional dose distribution measurements. As clinics move towards electronic imaging, the film processors that are critical for radiographic film use are being removed. Multi-point electronic dosimeters have recently been introduced and are being used for dose distribution validation. While the use of these devices is fast and convenient, they are limited to measuring single planes oriented normal to the incident beams and cannot be used in most geometric phantoms, the use of which are critical to treatment planning system commissioning. In addition to the measurement dimensionality, an important operating characteristic for dosimeters is the user's ability to characterize and monitor the dosimeter response. This has been possible with multipoint electronic dosimeters, but not higher-resolution single-use dosimeters such as radiographic or radiochromic film. We propose to develop a novel, reusable, high-resolution two-dimensional dosimeter with an effective atomic number (Z) close to water. This dosimeter will be a storage phosphor plate (SPP) consisting of low Z storage phosphor particles dispersed in a polymer binder. Our first aim is to develop a process for preparing low Z storage phosphor powders. Our second aim is to quantify the dosimetric properties and optimize the phosphor production process developed in aim 1. Our third aim is to produce a prototype SPP using a state-of-the-art tape-casting method. The successful completion of these specific aims will provide a quantitative two-dimensional dosimeter that can be used in existing geometric phantoms and that can be reused so that the dosimetry characteristics can be determined and monitored by the physicist.